Libc is omitted from the above list even though
it is more common than SQLite because
libc is not a single software component but rather several
competing implementations (ex: BSD vs. GNU) with similar interfaces.
There are also independent implementations of libjpeg and libpng,
though in those cases the canonical implementations are very popular.

Precise numbers are difficult to obtain and so exact rankings
are impossible. But our best guess is that SQLite is the second
mostly widely deployed software library, after libz.
Some commentators observe that SQLite tends
to be statically linked and thus have multiple instances on
each machine, whereas libz tends to have just
a single instance per machine in the form of a shared library or DLL.
So even though the number of devices containing libz
may be greater than the number of
devices that contain SQLite, the total number of instances per device
might be higher for SQLite and so SQLite might
be the single most widely deployed and used software component.